Controlling resource allocation

If a reservation job is given by a user (with the SECURE-RESOURCE-ALLOCATION) command), the system tries to reserve all the resources requested (devices, volumes or files) for this task.
If the requested resources are available and can be reserved for the task, the reservation job is completed and other user jobs can be processed.

If the reservation job cannot be executed at all or only in part, the job is entered in a queue (secure queue). Waiting jobs receive no resources (except possibly the collector task).

Collector task

The operator has the option of selecting one job in a secure queue for privileged handling. This means that the task stands at the head of the queue and is able to collect the resources requested. This task is known as the collector task. The commands START-RESOURCE-COLLECTION, MODIFY-RESOURCE-COLLECTION and STOP-RESOURCE-COLLECTION are available to the operator for controlling collector selection.

These commands enable the operator to execute the following functions:

• Starting COLLECTOR selection

  The operator activates the selection of a collector task by means of the START-RESOURCE-COLLECTION command. The system calculates a weight for each task in the secure queue in accordance with the following formula:

  W = T + N * U

  W	Weight;
  T	time; wait time the task has already spent in the secure queue
  U	urgency; this value is calculated from the task priority, the task with the highest priority having the lowest urgency and vice versa
  N	factor which is entered by the operator in the TIME-WEIGHT operand of the START-RESOURCE-COLLECTION command (default value is 10). The operator can influence the calculation of the weight by selecting factor N: If N is low, the wait time the task has already spent in the secure queue is assigned high significance. If N=0 is specified, the wait time is equal to the weight and the urgency has no influence on the calculation. If, however, N is high, the significance of the task priority increases for the calculation of the weight. For N=600 the weight is calculated almost exclusively from the urgency; the wait time is hardly significant in the calculation.

  After the system has carried out this calculation for all tasks in the secure queue, the task with the highest weight becomes the collector task. The collector task is placed at the beginning of the secure queue and can collect the resources requested. Once the collector task has collected all the resources it requested, it is removed from the secure queue, and the system recalculates the weights for the tasks remaining in the queue, whereupon a new task becomes the collector task.

• Excluding tasks from selection

  The operator can exclude a task from selection by means of the command MODIFY-RESOURCE-COLLECTION ACTION=*REMOVE-COLLECTOR. If the system determines a new collector task (see 1.), this task is not considered, i.e. it cannot become the collector task. If the task specified is the collector task at the time of exclusion, it loses its collector attribute and thus all resources which have been reserved up to this time.

• Admitting tasks for selection

  The operator can readmit a previously excluded task for selection (see 2.) by means of the operand ACTION=*ADD-COLLECTOR; This task is again considered by the system at the next collector selection.

• Declaring a task as the collector task

  The operator can declare a task as the collector task by means of the command MODIFY-RESOURCE-COLLECTION ACTION=*SET-COLLECTOR. If another task is the collector task, it loses its collector attribute and therefore the resources it has already collected. The task specified in the command becomes the collector task. This function is also possible without a previous START-RESOURCE-COLLECTION command.

• Terminating collector selection

  The STOP-RESOURCE-COLLECTION command enables the operator to terminate the collector selection started with the START-RESOURCE-COLLECTION command (see 1.). If a task is the collector task, it does not lose its collector attribute and can continue to collect the resources it requested. If the operator withdraws the collector attribute from this task (see 2.) or the collector task can collect all resources requested, no new collector task is selected by the system.